More than any other type of well, horizontal wells, sometimes referred to as laterals, need to be planned at the reservoir level with knowledge of where the drilling pad will be located. Likewise, the location and spacing of the horizontal wells must be taken into account when planning the positions of these drilling pads. In addition to the well positions, spacing, length and the like, boundaries and hazards must also be taken into account when positioning the drilling pads. Hazards can come in the form of subsurface hazards such as faults or shallow gas, or surface hazards such as roads, buildings, bodies of water, pipelines, railroads, environmentally sensitive areas and the like. In addition to surface hazards, the terrain itself is not always conducive to drilling. It might be too high, or contain too much slope so that the site preparation becomes too expensive.
As horizontal well field development has expanded over the last several years, it has been discovered that horizontal well targeting algorithms work much better if the laterals are positioned based upon existing pad locations. And, the pad locations produce better laterals if they are spaced appropriately based upon the laterals for which they are intended. Because of this interrelationship, techniques designed to do a throw away targeting of laterals, spot locations based upon those laterals, delete the laterals and redo the targeting based upon those computed locations produce decent results in simple areas but less effective results in regions where the terrain places severe restrictions on where drilling pads may be located. In order to address the less effective results, techniques have been employed where lots of pad locations are identified in areas where the terrain allows, then an optimal subset of those pad locations is determined. Although this technique has produced decent results, they are not optimal results wherein the pad location locations are evenly distributed over the entire field.
Attempts have also been made to use targeting algorithms for standard injector/producer patterns, such as line drive, to generate patterns that can be exported and reimported as platform locations, however, have been found to be less than optimal because the targeting algorithms are intended to create patterns that fill the boundaries with the maximum number of targets, whereas with drilling pads, maximum coverage with the fewest pad locations is desired.
Other conventional approaches have been patented such as the technique described in U.S. Pat. No. 7,200,540, which discloses an automated method for generation of platform locations and includes computing a maximum number of targets to be assigned to each respective user specified platform, selecting a possible set of platforms, validating the set of possible locations by comparing against exclusionary polygons and determining the best set of platform locations. Another patented technique is described in U.S. Pat. No. 6,549,879, which discloses a method for automated positioning of pad locations for drilling wells in a two stage method, wherein the drilling pads are positioned assuming wells can be only vertical and are then examined for optimized horizontal and deviated completions. Although these patented and unpatented techniques may produce acceptable results, they may be less than optimal for positioning drilling pads in consideration of the location and spacing of each horizontal well, the boundaries and surface/subsurface hazards.